1. Field of the invention
This invention relates to a back focus adjusting mechanism provided in imaging cameras.
2. Description of the Related Art
JP-A-2000-165733 discloses aback focus adjusting mechanism for an imaging camera. The disclosed mechanism comprises a rotatable adjusting ring and a cam mechanism actuated with rotation of the adjusting ring so that an imaging element unit is moved along an optical axis of an optical system. A leaf spring applies a pressing force to the adjusting ring when the adjusting ring reaches an adjustment position, whereby the adjusting ring is locked at the adjustment position.
In the above-described back focus adjusting mechanism, however, a locking screw is screwed into a camera housing from outside so that the leaf spring is deflected by the locking screw, whereupon the adjusting ring is locked at the adjustment position. Accordingly, the back focus adjustment requires a tool, such as a screwdriver, for driving the locking screw, resulting in problems in the speediness and operability.
Therefore, an object of the present invention is to provide a back focus adjusting mechanism which can overcome the foregoing problems and is easy in the operation for back focus adjustment.
The present invention provides a back focus adjusting mechanism for an imaging camera Including a camera housing, a lens mount protruding in the camera housing and including a cylindrical portion formed with a guide, an imaging element and an imaging lens. The back focus adjusting mechanism comprises a coil spring provided around the cylindrical portion of the lens mount, an imaging element holder holding the imaging element so that the imaging element is moved along an optical axis of the imaging lens by the guide of the lens mount, an adjusting ring provided with a cam the imaging element holder engages, a positioning holder fixed in the camera housing and positioning the adjusting ring so that the adjusting ring is rotatable around the cylindrical portion of the lens mount, the imaging element holder engaging the cam by rotation of the adjusting ring being moved, a spring member pressing the adjusting ring against the positioning holder and fixed in the camera housing, and a knob member operated outside the camera housing. The adjusting ring is fixed at an adjustment position while being subjected to a pressing force of the spring member by the knob member.
In the above-described mechanism, the imaging element holder abutting the cam by the rotation of the adjusting ring is moved so that the back focus of the imaging camera is adjusted. In order that the adjusting ring may be fixed at the adjustment position, the knob member is operated outside the camera housing so that the adjusting ring is kept pressed against the positioning holder. Thus, the adjusting ring can be fixed at the adjustment position only by operating the knob member outside the camera housing. Consequently, the back focus adjustment can be carried out readily and quickly without use of a tool such as a screwdriver.
In a preferred form, the camera housing has a side wall formed with an opening, and the mechanism further comprises a slider provided on an inner wall of the camera housing so as to be vertically slid and including a pressing boss, the knob member being mounted on the slider so that the knob member is operated through the opening. In this construction, the slider is slid so that the spring member is pressed by the pressing boss, whereby the adjusting ring is fixed at the adjustment position while being subjected to the pressing force of the spring member. Accordingly, the adjusting ring can be fixed at the adjustment position only by sliding the slider without use of a tool such as a screw driver readily and quickly.
In another preferred form, the spring member comprises a leaf spring including a spring body and a pressing portion continuous from the spring body and bent into a U-shape, the pressing portion being abutted against the adjusting ring. Since the spring member comprises the leaf spring, a mounting space for the spring member in the camera housing can be reduced.